2.0 Analysis 2.1 Terminal Control The Learjet flight crew filed a flight plan altitude of 5,000 feet asl for their flight from LBPIA to Hamilton, and their requested altitude of 5,000 feet asl was displayed on the ADDS equipment. When coordination between Hamilton sector and the Terminal Data position occurred for the Convair, 6,000 feet asl was given with respect to the Learjet, which was contrary to procedure. The Terminal Radar controller cleared the Learjet to 5,000 feet because the ADDS indicated that the Learjet flight crew had only requested 5,000 feet and because he was aware that 6,000 feet had been coordinated for the Convair to proceed to LBPIA. 2.2 Hamilton Control The Hamilton sector controller re-instructed the Convair to maintain 5,000 feet asl when he observed the Learjet depart LBPIA. He anticipated that the Learjet was going to enter his area of responsibility at 6,000 feet asl, which is the established procedure between Terminal and Hamilton sectors and is in accordance with the ANOs. He did not observe on the ADDS that the Learjet flight crew had only filed for 5,000 feet asl on their flight plan. 2.3 Coordination A lack of coordination existed when Hamilton Sector did not communicate to Terminal that the Convair flight crew had been re-instructed to maintain 5,000 feet instead of 6,000 feet as had been previously coordinated. 3.0 Conclusions 3.1 Findings The Learjet flight crew filed a wrong-way altitude of 5,000 feet asl on their flight plan. Contrary to procedure, the Terminal Data controller coordinated 6,000 feet asl with the Hamilton sector controller for the Convair. Contrary to procedure, the South Departure controller cleared the Learjet to 5,000 feet asl. The Hamilton sector controller did not observe the Toronto departure (Learjet) on the ADDS. The Hamilton sector controller did not coordinate or communicate to the Terminal controller that the Convair had been re-instructed to maintain 5,000 feet. The Hamilton sector manual did not stipulate the procedure for aircraft departing Hamilton and landing at LBPIA. 3.2 Causes An air proximity event occurred because the Terminal controllers did not follow procedures as prescribed in the Terminal sector manual, and there was a lack of coordination between the Terminal and Hamilton sector controllers. The Board has no aviation safety recommendations to issue at this time.4.0 Safety Action The Board has no aviation safety recommendations to issue at this time.